1. Field of the Invention
This invention relates in general to a method of repositioning teeth for use in orthodontic treatment. Particularly, this invention relates to the use of orthodontic appliances for producing tooth movements. More particularly, this invention relates to the use of a plurality of elastic repositioning appliances for producing such tooth movements.
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as xe2x80x9cbraces.xe2x80x9d Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After they are bonded to the teeth, periodic meetings with the orthodontist are required to adjust the braces. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time consuming process requiring many visits to the orthodontists office. Moreover, from a patient""s perspective, they are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances may comprise a thin shell of elastic material, referred to as an xe2x80x9calignerxe2x80x9d, that generally conforms to a patient""s teeth but is slightly out of alignment with the initial tooth configuration. Placement of an aligner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually move the teeth through a series of intermediate arrangements to a final desired arrangement. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT application WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
Systems of preformed aligners employing technology described in U.S. Pat. No. 5,975,893, are commercially available from Align Technology, Inc., Santa Clara, Calif., under the tradename Invisalign(copyright) System. Align Technology, Inc., is the assignee of the present application. The Invisalign(copyright) System relies on designing and fabricating at least most of the aligners to be worn by the patient at the outset of treatment. The design of the aligners relies on computer modeling of a series of successive tooth arrangements, and the individual aligners are designed to be worn over the teeth and to elastically reposition the teeth to each of said tooth arrangements. Usually, the set of aligners which is designed and fabricated at the outset of the treatment is able to successfully reposition the teeth to a final desired arrangement. In some cases, however, the treatment deviates from the planned movement stages making continued treatment with the previously provided set of aligners difficult or impossible. Such deviations can arise from biological variations in the individual patient, poor patient compliance, or other factors. The deviations will usually become apparent when the next aligner to be worn in the set of successive aligners does not fit. A poor fit indicates that the tooth arrangement has not progressed to the desired intermediate stage and that the teeth are not ready for the next aligner.
When such deviations occur, the response has usually been to start over with whatever actual tooth arrangement that has been received being the starting point. Aligners are then planned and fabricated to bring the teeth from the actual intermediate arrangement to the desired final arrangement, which is usually the same final arrangement as was the target of the original set of aligners. Starting over, however, can be inefficient and wasteful. Relatively large numbers of aligners can be required, and the remaining aligners in the original set will usually be wasted.
For these reasons, it would be desirable to provide alternative and/or improved methods for making mid-course corrections in orthodontic treatment utilizing sets of aligners or other repositioning appliances which are removable and successively worn by a patient to effect a course of orthodontic treatment. It would be particularly desirable if such methods did not require disposal of all or some of the aligners from the original set and were relatively easy to implement with minimum patient inconvenience. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
U.S. Pat. No. 5,975,893, and published PCT application WO98/58596, have been described above. Co-pending application Ser. No. 09/616,830, relates to the fabrication of orthodontic aligners having varying elastic moduluses. The full disclosures of each of these patents and pending applications are incorporated herein by reference.
According to the present invention, an improved method for repositioning teeth is provided. The method for repositioning generally relies on use of an original set of removable positioning appliances, typically aligners as described in U.S. Pat. No. 5,975,893, the full disclosure of which has been previously incorporated herein by reference. The aligners or other appliances are shaped to move teeth through a plurality of predetermined successive arrangements corresponding to the shape of each appliance. That is, the appliances will be configured to apply repositioning forces to the teeth so that the teeth are moved to an arrangement which closely conforms to the unstressed geometry of the aligner. Thus, after a patient has completed wearing any individual aligner or other appliance, it will be expected that the tooth arrangement will match the shape of the aligner or appliance and that the teeth will be ready to receive a next successive aligner or other appliance. The next successive aligner will be shaped slightly differently from the immediately prior aligner, and it is this difference in shape that will move the teeth still further to their next arrangement. Wearing of successive aligners or other appliances thus can effect an entire course of orthodontic treatment as the teeth are moved through a series of predetermined successive arrangements.
In the case of the Invisalign(copyright) System, an original set of aligners will be designed and fabricated at the outset of treatment. The individual aligners will then be available to the patient and/or treating professional so that the aligners may be worn and exchanged as the teeth progress through the expected successive arrangements. Usually, each individual aligner is worn for about two weeks corresponding to one stage of treatment. This period, of course, can vary from several days to several weeks or longer, depending on the individual treatment plan selected for the patient.
The present invention is concerned with those patients who do not progress through treatment as expected and planned. In some cases, an actual tooth arrangement achieved by a patient will differ from the expected tooth arrangement corresponding to the shape of a particular appliance. Such deviation from the expected treatment will usually become apparent when the patient tries to wear the next aligner in a series. If the actual tooth arrangement differs to any significant degree from that which was expected, the next aligner in series will typically not be able to seat properly over the teeth. Such inability to fit or seat on the teeth provides an indication that the actual tooth arrangement which has been achieved at that point in treatment differs from the expected tooth arrangement which should have been achieved after treatment with the immediately prior appliance.
The present invention provides methods for correcting such deviations in the planned and expected treatment path by providing at least one additional removable appliance which has a shape or a compliance selected to move the teeth from the actual (but deviant) tooth arrangement back to one of the predetermined successive tooth arrangements. The tooth arrangement to which the teeth are reconfigured will often be the arrangement to which they should have been at the end of the just completed stage. Alternatively, the arrangement could be any one of the successive stages, usually five stages or fewer beyond the just completed stage, more usually four stages or fewer, and typically no more than three stages beyond the just completed stage.
For the most minor deviations, it will be often be sufficient to provide an aligner or other tooth positioning appliance which has the same geometry as an aligner from the original set, usually as the next aligner in the series. While the aligner will have the same shape, it will be more compliant or elastic so that it can fit and seat over the teeth, even though the shape is further from the geometry of the actual tooth configuration than had been originally intended. The more compliant aligner can then bring the teeth back toward the target configuration for that stage of treatment. Optionally, two or more compliant aligners having the same geometry could be employed, where successive ones of the new aligners will be incrementally stiffer or more rigid to continue to move the teeth toward the target configuration.
The use of additional aligners having the same shape as an original aligner, but which are more compliant, is particularly advantageous since it simplifies design and fabrication of these aligners. The shape or geometry of the aligner would already have been planned during the initial treatment planning process (as described in detail in prior patent U.S. Pat. No. 5,975,893, which has been incorporated herein by reference), and it is necessary only to mold or otherwise fabricate the aligner out of materials having different elasticities. The ability to form aligners having different elasticities is described in detail in co-pending application No. 09/616,830, the full disclosure which has previously been incorporated herein by reference.
In some instances, however, it may not be possible and/or desirable to use aligners having the same geometry as an original aligner to bring the teeth back on to the intended treatment path. In such cases, it will be necessary to design one or more aligners having different shapes in order to move the teeth back from their actual configuration to a tooth arrangement corresponding to one of the appliances from the original set of appliances. Such treatment planning can be performed, for example, by the methods used for the original treatment planning as described in U.S. Pat. No. 5,975,893, the full disclosure of which has been incorporated herein by reference. That is, the actual tooth arrangement, i.e., the tooth arrangement which has been actually achieved in the treatment thus far, will be digitally modeled. Based on the digital model of the actual tooth configuration as a starting point, and a selected one of the target intermediate stages as an ending point, a series of one, two, three, four, or five, or more, new aligners or other positioning appliances can be designed using the computer-aided design protocols described in the patent. Once the new aligner designs are finalized, the digital models of the aligners can be used to fabricate actual aligners using the previously described methods.
For both compliant aligners and differently shaped aligners, the patient will wear the corrective aligners until the teeth have returned to an arrangement which allows an aligner from the original set of aligners to be worn and to move teeth to the next successive arrangement. Depending on the degree of deviation, it may take one, two, three, four, five, or even more, additional aligners or other positioning appliances to provide the desired correction. The corrective aligners or other appliances might be worn from several days to several weeks, or more, until the desired correction is achieved.